Calculate bolt torque from preload, bolt diameter and a typical nut factor, or solve for preload, diameter or K, with a gasket seating-load option.

Typical values for steel bolts; friction varies, so the torque is an estimate. Use your fastener makerโ€™s K when you have it.

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Gasket Torque Formula

The following is a rough empirical torqueโ€“preload approximation. F is the force on one bolt and D is its nominal diameter. Pick a typical nut factor or enter one established for the actual fastener, lubrication and surfaces; the calculator does not select a safe preload.

Tg = F ร— D ร— k / 1000
  • Where Tg is the Gasket Torque (N-m)
  • F is the bolt load / preload force (N) 
  • D is the diameter (mm) 
  • k is the nut factor (k-value) 

Multiply per-bolt preload by nominal bolt diameter and nut factor, dividing millimeters by 1,000 to obtain meters. The relation is T โ‰ˆ K F d. Techneticsโ€™ metal-seal catalog describes this as a rough estimate and notes the dependence on joint and friction conditions. It does not verify bolt/flange strength or sealing performance.

How to Calculate Gasket Torque?

The examples below demonstrate arithmetic only; their loads and nut factors are not recommended assembly values. For the separate annular model, area A = ฯ€(ODยฒ โˆ’ IDยฒ)/4, seating-only load W = A ร— specified seating stress ร— specified multiplier, and equal per-bolt load is W divided by bolt count. Full-annulus contact and equal loading are assumptions. Pressure end load, effective gasket contact width, relaxation and joint limits require separate design review and a joint-specific assembly procedure. See the scope of ASME PCC-1.

Example Problem #1

  1. First, determine the bolt load / preload force (N). In this example, the bolt load (N) is given as 50,000.
  2. Next, determine the diameter (mm). For this problem, the diameter (mm) is given as 20.
  3. Next, determine the nut factor (k-value). In this case, the nut factor (k-value) is found to be 0.20.
  4. Finally, calculate the Gasket Torque using the formula above: 

Tg =F*D*k / 1000

Inserting the values from above and solving yields: 

Tg =50,000*20*0.20 / 1000 = 200 (N-m)

Example Problem #2

Using the same method as above, determine the variables required by the equation. For this example problem, these are provided as:

bolt load (N) = 60,000

diameter (mm) = 40

nut factor (k-value) = 0.18

Entering these given values yields: 

Tg =60,000*40*0.18 / 1000 = 432 (N-m)